Imaging systems are arranged to output an image. They may comprise printing or display systems, wherein an output is either a printed or displayed image. In these cases, color data for the image may be represented in a first color space and it may be necessary to map this color data to a second color space that is used to produce the output. To do this a color mapping may be used. In a halftone imaging system, the color mapping may be followed by a halftoning process so as to reproduce a continuous tone image represented in the second color space using a series of dot shapes. This may allow the continuous tone image to be output on an imaging device with a discrete number of output states, e.g. a printer capable of depositing a discrete number of colorant drops per output pixel. The result of this process is a halftone color separation. Each halftone color separation may have desired color properties in some part of a color space; however, it may not provide desired color properties across the whole of the color space.